Apparatus for sound reproduction



Mig H5 1929- K. a. MARSHALL, 31,734,999

APPARATUS FOR SOUND REPRODUCTION Filed May 6l 1926` C5 Sheets-Sheet l Aug. 13, 1929. K. l. MARSHALL 1,724,099

APPARATUS F'OR SOUND REPRODUCTON Filed May 6, 1926 3 sheets-Sheet 2 l N VEN TOR. Men/M777 l Mcy/fs/m/ BYM ATTORNE Aug w, 1929 K. l. MARSHALL 'i,724,09

APPARATUS FOR SOUND REPRODUCTTON Filed May 6, 1926 5 Sheets-Sheet 5 INVENTR. Hen/767% f Mar/ a/ A TTORN lll lil

ldatented lidi9 limiti.

APPARATUS FR Slthilll REPRDUGTIN.

implication le. Ylliay 6, 19%. Serial life. l0?,064.

This invention relates to the electrical reproduction of sound trom phonograph records and the main object ofthe invention is to provide means whereby the maximum number of parts oli an existing phonograph ot the mechanically reproducing type may be utilized in such electrical reproduction.

A further object of the invention is to provide an electrical reproducing device which may be conveniently applied to the ordinary tone arm of an existing phonograph ol the mechanically reproducing type.

Ai further object et the invention is to provide a device which may be appliedto the tone arm of a phonograph and which comprises both a transmitting device for producingn electrical impulses corresponding to the phonograph record and also a receiving or loud speaking device for converting amplified electrical impulses into sound., the connection to the tone arm being made in such manner that such tone arm serves not only to support said device in position to engage the record but also to receive and amplify the sound produced bysaid receiving or loud speaking device.

A further object ot the invention is to provide a construction in which the reproducing element and the loud speaking element are so mounted with respect to one another that the latter serves to partially counter balance the former and thereby decreases the effective Weight with which the phonograph needle mounted in the reproducing device bears upon the record.

The accompanying drawings illustrate embodiments of my invention and referring thereto: l,

Fig. 1 is a semi-diagrammatic plan view of a phonograph provided with means for electrical reproduction of sound according to my invention.

Fig. 2 is a plan view of a device according to my invention applied to the tone arm of a mechanically reproducing phonograph.

Fig. 3 is a side elevation of the parts shownmin Fig. 2.

Fig. 4 is a vertical section of the reproducing element on line 4,-4 in Fig. 5.

Fig. 5 .is-.a vertical section on line 5-5 in Fig. 4.

Fig. 6 is a section on line 6 6 in bFig. 4.

Fig. 7 is a vertical section ot the loud speaking device on line Z- in Fig. 2. v

Fig. 8 is a section on line 8-8 in Fig. Q,

showing the means tor mounting the device on the tone arm.

Fig. 9 is a wiring diagram of an electrical amplifying means suitable for use in convnection with my invention.

ln Fig. l l have shown an ordinary phonograph cabinet l provided with a record carrying plate or disk 2 and with means (not` shown) for driving said record-carrying plate and for stopping and starting and regulating the speed ol said driving means. ln phonographs of the mechanically reproducing type it is customary to provide a hol low tone arm 3., mounted as at 4 so as to swing .in a horizontal arc across a phonograph record 5 on the record-carrying plate.' lt is also customary to provide a sound bon for the mechanical production of sound from the phonograph record, such sound box being mounted for example by meansof a U-shaped hollou7 connecting tube, which is mounted in a laterally7 extending tubular ,bearing means 8 at the end of the tone arm so that the sound produced in sound box 6 passes through said connecting tube and thence into tone arm." 3l and into the usual built-in phonograph horn, not shown, which is in communication with the base of tone arm 3.

According to my invention the abovementioned connecting arm and sound box may be removed from the end of such tone arm and a device comprising electrical reproducing and loud speaking means is substituted therefor. Such device may com,- prise a tubular portion 10 adapted to lit within the lateral tubular bearing means 8 at the end oi the tone arm, said tubular member 10 projecting at one end to form a hollow arm as indicated atvll, at the end of which is provided a loud speaking device 12. Tubular member l() is provided v 1th an opening 9 in its rearward wall communieating with the interior of tone aim 3, so asto permit passage of sound waves there through.

The other end of tubular member 10 may project somewhat beyond the bearing means 8 as indicated at 13, and upon said proiecting portion may be journalled an arm so as to swing in a substantially vertical plane, said arm carrying at its outer end an electrical reproducing device 15. The tubular member 10 and the projecting portion 13 thus constitutes a bearing member. In order to prevent lateral movement of arm 14 with respect to its bearing means 13 while permitting swinging movement thereof, the, bearing portion 16 of said arm Inay be provided with" an inwardly extending pin 17 engaging in an annular groove or slot 18 in the member 13. The groove 18 communicates at one end as indicated in Fig. 8 with an outwardly extending groove 19 so as to permit entrance of pin 17 into the groove 18 in assembling the device. The upper end 20 of groove 18 serves as a stop means for pin 17 as shown in Fig. 4, when the reproducing device is lowered into playing position, for the purpose hereinafter described. A retaining screw 21 having a flanged head 22 is screwed into t-he outer end of bearing portion 13 so as to cooperate with a flange 45 on member 1() to retain the parts in assembled position, there being however suflicent play between the bearing portion 17 ot' arm 14 and bearing means 8 and flange 22 and also between flange 45 and member 8 so as to permit free vertical swinging movement of arm 14.

The transmitting or reproducing `device indicated at 15 may comprise, as shown in 'FigsI 4, 5, and 6, a cylindrical casing 23 within which is mounted a permanent magnet 24, said magnet being supported in any suitable manner for example by securing the same to supporting plate 25 which forms the lower end of cylindrical casing The magnet 24 may be formed for example as a ring extending around the inside of the casing 23 and having its two oppositely charged .ends 27 and 28 overlapping but spaced from one another. U-shaped pole pieces 29 and 31 may be secured to the respective ends 27 and 28 of said magnet and an armature 32 may be mounted for rocking motion between said pole pieces. Said armature may be mounted for example by means of flexible suspension wires 33 and a light wire spring 34 may be so mounted as to exert a downward pressure upon one end of said armature so as to preserve a slight tension on the suspension wires 33.

Beneath the supporting plate 25 is mounted a substantially rigid rocking member comprising for example a bridge or plate 36 anda needle carrying member 37 integrally or rigidly secured to said bridge. The ends of the bridge 36 may be mounted between resilient supporting pads or blocks 38 consisting for example of cylindrical pieces of rubber or other yielding or resilient material and said bridge may be clamped vbetween said pads by means of brackets 39 which may be mounted for example on a second supporting plate 4t). Said brackets serve to hold the supporting pads 38 and bridge 3G bctween the brackets and supporting platesl L'ttl with the desired degree otI firmness. ln order to prevent lateral displacement ot the supporting pads 38 suitable centering projections 4l may be providml on both the brackets and the supporting plates` for cxamplc by 11p-setting or puntbing the metal at these points.

Needle carrying member 37 may bc provided with a suitable shaped recess for rcceiving a phonograph nccdh` or stylus 12 and a set screw 43 may be provided for securing said needle within sai'd recess. A link nicmber 44 may extend through openings 3l) and 35 in plates 25 and 4() and may bc secured at its ends, by soldering or otherwise, to armaturel 32 and bridge mcmber 3G so as to transmit. rocking motion of said bridge to said armature as hereinafter described. ln order to permit lengthwise adjustment of the link member with respect to the rocking member, the bridge 36 may be formed or provided with a bent-over portion 4G extending back above or beneath and somewhat beyond said bridge, and the lower end of said link member may be secured to the cnd of said benl-over portion. Said bent-ovei"portion is formed of metal having a certain amount of resiliency and an adjusting screw 47 passes through the bridge member and screws into the bent-over portion so as to provide for adjustment of said bent-over portion toward or away from the bridge.

A wire coil 48 may be provided around the armature member 32 in such manner that changes in the magnetic flux in said armaturc member due to rocking motion thereof between thc pole pieces 29 and 31 causes electric currents or impulses to be set up within said coil. Suitable terminal means such as insulated binding posts 49 and 51 may be mounted on .supporting plate 25 and the two ends of coil 48 may be secured to said binding posts by means of wires 52 and 53 respectively. i

A cover plate 54 may be provided for protecting the rocking member and other parts above described. said cover plate together with supporting plates 25 and 40 being se cured to the casing 23 in any suitable manner by means of screws 56. Said cover plate may have an opening 57 through which the needle carrying member 37 projects and through which access may be had to adjusting screw 47.

Thilo I have described one particular form of reproducing element which may be used in connection with my invention I wish it to be understood that any form of electrical phonograph reproducer may be used in place of that above described. The constructionof the reproducing unit above de- 62 winch is connected in any suitable mannerY to the end of the hollow arm 11 and which has an opening. 63 opening into said arm. lVithin `casing 61 is provided a supporting plate 64 upon which is mounted a permanent magnet 65 formed for example in the same manner as the magnet of the reproducing unit above described and providedin similar manner with pole pieces 66 and '67 se-i cured to its respective ends 68 and 69 and with an armature 71 supported by suspension wires 72 and provided with means such as spring wire 73 for preserving tension on supporting Wires 72. Coil 74 is provided around armature 71, with its two ends connected by wires 76 and 77 to binding posts 78 and 79 mounted within casing 61. A diaphragm 81 of suitable material such as mica or thin metal is mounted between supporting plate 64.- and cover plate 62, and the center of said diaphragm is connected to one end of armature 71 by means of link 82 which extends through an opening 83 in supporting plate 64. Any suitable means may be provided for. supportingr the loud speaking unit when it is not held up by the reproducing unit as hereinafter described such supporting means comprising for example a bracket secured' to tone arm 3 and extending beneath the loud-speaking unit.

Any suitable means of electrical amplification may be used in connection with my invention. For example vthe thermioniotubel amplifier shown in Fig. 9 may be utilized for this purpose. The amplifying system there shown comprises thermionic vacuum tubes 86 and 87, each provided with filament 88, grid 89, and plate 90, and further comprises step-up transformers 70 and 91, transformer 70 having its secondary winding connected to the grid of the first thermionic tube 86, and transformer 91 having its primary winding connected to the plate of the first thermionic tube 86 and its secondary Winding connected tothe grid of the second therniionic tube 87. Suitable connections maybe provided, as indicated, between the Various parts of the above described amplifying means and the usual A, B, and C batteries, for supplying the necessary electric 'current or voltage thereto.

The reproducing unit may be connected by Wires 98 and 94 to the input terminalsof the amplifying system for example in this case to the primary terminals of transformer 70. A rheostat or adjustable resistance means 95 may be included in one of the wires 93 or 94 for the purpose of regulating the current flow therein and hence regulating the volume of sound produced. The output terminals of the amplifying system may be connected by wires 96 and 97 to the loudspeaking receiving unit 12 above described. The amplifying system above described may be a separate amplifying system and may be located at any suitable point within or convenient to the phonograph. For example in Fig. 1 the electrical amplifier is shown.

located within a separate box or cabinet 98 located adjacent the phonograph cabinet.. The wires 93, 94, 96, and 97 leading to and from the amplifier may be enclosed in a suitable connecting cable or cord 99 which may be brought into the phonograph cabinet in any suitable manner and may extend along beneath the tone arm 3, being supported thereon in suitable manner, as by means of supporting clamps or brackets 101. Said connecting cable or cord may have two branches 102 and 103, theformer containing wires 93 and 94 and extending through an opening 105 in the side of casing 23 so as to permit connection of Wires 93 and 94 to binding posts 49 and 51, and the latter extending through an opening 106 in the casing 61 of the loud-speaking receiver so as to permit connection of wires 96 and 97 to binding posts 78 and 79.

In applying the above described device to the mechanically reproducing phonograph tlie sound box 6 and connecting tube 7 mayl be removed and thertubular portion 1() of the device inserted within the tubular bearing member 8 at the end of thetone arm. The repioducingflevice is then mounted on the other end of the tubular member 10 by in sei-ting pin 17 through groove 19 and into groove 18, the loud-speaking receiver being necessary lifted oli' of its support 75 and swung upwardly so as to permit said pin to be so inserted. Retaining screw 21 is then screwed into position to hold the members in the position shown and the electrical connections are made as above described.

In the operation of the above-described apparatus a phonograph record indicated at 5 is placed on the record-carrying plate 2 and is set in rotation at the proper speed in the usual manner.. The reproilucing element 15 is then lowered onto the record so as to cause needle or stylus 42 to engage and traverse the grooves ofthe record. lt will be seen that when the reproducing device is thus lowered onto `the record the pin 17 comes into engagement with stop means 20 at the upper end of the groove 18 slightly before the` needle or stylus Ii2 erigages the record so that the last portion of the dow-n.-`

ward motion of the reproducing device causes the loud-speaking element 12 to be lifted off of its supporting means 75. The weight ot theloud-speaking element thus serves to partly ctumterbalance the weight ot the reproducing element, these two elements being at this time pivoted about the substantially horizontal axis of tubular member 8. A very light pressure of the needle or stylus upon the phonograph record is thus obtained in spite ot' the considerable'weight of the reproducing device, such light pressure being desirable in that it minimizes scratching and other objectionable noises and permits the needle or stylus to vibrate freely.

The undulations or impressions in the groove ot the record which is adapted to be used with the particular reproducing.,r device shown extend transversely ot the groove so as to cause the point of the needle to move rapidly back and forth in the direction of `such undulations and such motion ot the needle causes rocking motion of bridge 36. Such motion is transmitted through link member 44 to armature 32 which is thus All) '31 so that an alternating magnetic flux is created Within said armature. Small alternating or variable electrical impulses corresponding in frequency and magnitude to t-he vibration of the armature and hence to the movement of the needle are thus induced in coil 48 and such current is supplied through wires 93 and 94 to the amplifying system above described. The strength of the current impulses so supplied may be adjusted by operation of rheostat 95y so as to give the desired volume ot sound production.

It is believed unnecessary to describe in detail the operation of the amplifying system since such operation is well-known and forms no essential feature of this invention. The operation of such amplifying system is suchl however as to produce within the output circuit including wires 96 and 97 alter.

nating or variable current impulses correspending to but of much greater intensity than the electrical impulses initially set up in coil 48. Such electrical impulses pass through coil 74 cause an alternating magnetic luXing to be set up in armature 71 of the loud-speaking receiver 12 so that the opposite ends of said armature are alternately charged positively and negatively and are caused to move toward and away 'from the respective pole pieces 66 and 67. The resulting rocking motion of armature 71 is transmitted through link member 82 to diaphragm 81 causing said diaphragm to vibrate and produce sound waves corresponding in frequency, intensity, and modulation to the original impressions or undulations on the phonograph record and hence to the original sound which it is desired to reproduce. Such sound waves pass through the tubular arm 11 into the interior of the member and thence out through opening 9 into the tone arm 8 and through said tone arm and the phonograph horn to the ears of the listeners.

Then it is desired to remove the record, the reproducing unit may be lifted off the record. When lifted beyond a certain point` the receiving unit 12 comes to rest upon supporting means 75, and in the further upward movement of the reproducing unit, pin 17 moves in groove 18 and the reproducing unit moves independently of the receiving unit. In order to permit changing ot the needle or stylus, the reproducing unit may be swung back and over so as to rest upon the tone arm 3.

The application of the device according to my invention to a mechanically reproducing phonograph in order to enable the same to reproduce sound electrically is ot great advantage as it is well-known that the reproduction of sound from a phonograph record can be accomplished much more perfectly through the use of an electrical reproducing device associated with electrical amplifying means and a loud-speaker connected thereto than by means of the ordinary mechanically actuated diaphragm or sound box.

It is to be understood, as above mentioned, that any suitable type of electrical reproducing device adapted to produce electrical impulses corresponding to the impressions of a phonograph record and any suitable means Jfor producing sound in response to current impulses supplied thereto may be employed in connection with my invention instead of the particular reproducing and receiving elements above-described. Furthermore many modifications may be made in the manner of mounting said devices with respect to one another and with respect to the tone arm of the phonograph, it being essential however to my invention that said two elements are so mounted that the receiving element partially counterbalances the reproducing element when in playing position and that the tone arm of the phonograph serves not only to support both of said elements but also to convey the sound produced by the receiving element through the phonograph horn. It will accordingly be understood that in applying my invention to phonographs having other types ottone arms than the above described suitable modifications may be made in the means of mounting the reproducing and receiving elements so as to conform to the shape and construction of said tone arm while preserving the above mentioned essential relation. It is to be further understood that the reproducing element may be so constructed as to provide for movement or vibration of the. needle or stylus in any desired direction corresponding to the direction of the undulations of the phonograph records with which it is to be employed.

I claim:

l. An apparatus for sound reproduction comprising supporting means mounted to swing horizontally across and above a phonograph record, an electrical reproducing device pivotally mounted on the outer end` of said supporting means, and an electrical receiving device pivotally mounted on the outer end of said supporting means, said reproducing device and said receiving device being mounted to swing about a common substantially horizontal axis and being mounted at opposite sides of said aXis and being mechanically interconnected in such manner that the receiving device partially counter-balances the reproducing device.

2. In combination with the tone arm ot' a phonograph, said tone arm being mounted to swing horizontally across and above a phonograph record, an electrical receiving device mounted yat the outer end ot' said tone arm so as to swing about a substantially horizontal axis, means t'or directing sound from said receiving device into said tone arm, and an electrical reproducing device also mounted at the end of said tone arm so as to swing about the aforesaid axis, said reproducing device and receiving device being ilocated at opposite sides ot' said axis, and said reproducing device being free to swing upwardly independent of said receiving device and having means adapted to engage means connected to said receiving device, upon lowering the reproducing device into position to engage a record, so as to Cause the receiving device to partially counter-balance the reproducing device.

3. An apparatus comprising in combination with the tone arm of a phonograph, liXed supporting means secured to said tone arm, an electrical receiving device pivotally mounted at the outer end of said tone arm so as to swing about a substantially horizontal axis and in such position as to rest when lowered, upon said fixed supporting means, means for directing sound from said 'receiving device into said tone arm, an electrical reproducing device pivotally mounted at the end of said tone arm to swing about said airis, said reproducing and receiving device being mounted at the opposite sides ot said axis, and means mechanically interconnect ing said reproducing and receiving devices in such manner as to permit the reproducing device to be swung upwardly independently of the receiving device so that the receiving device is lowered into position on said fixed supporting means while causing the reproducing device when lowered into a certain position to lift the receiving device off of said lixed supporting means in such manner as to cause said receiving device to partially counterbalance the reproducing device.

4. In combination with a phonograph tone arm having a substantially horizontal tubular member at its outer end, a hollow arm having a portion adapted to t rotatably within said tubular member and opening into said tone arm, an electrical receiving device connected at one end of said hollow arm to direct sound into said hollow arm, an electrical reproducing device mounted to swing in a substantially vertical plane on said hollow arm and having means for carrying a phonograph needle, and means connected to said reproducing device and adapted, when the reproducing device is lowered beyond a certain point, to engage means connected to said hollow arm so as to cause the receiving device to move with the reproducing device and partially counterbalance the same.

5. An apparatus ior attachment to phonographs comprising a bearing member provided with a portion adapted for mounting on the tone arm of a phonograph and with a hollow arm having means for communication with said tone arm, an electrical receiving device mounted on said hollow arm to direct sound into the same, an electrical reproducing device mounted to swing on said bearing means and having means for carrying a phonograph needle, and means connected respectively to said bearing member and to said reproducing device and adapted to permit limited swinging movement of said reproducing device independently of said receiving device and to engage one another when the reproducing device is swung beyond a certain point so as to cause the receiving device to swing with the reproducing device.

6. An apparatus for sound reproduction comprising supporting means, an electrical reproducing devicevpivotally mounted on said supporting means, an electrical receiving device pivotally mounted on said supporting means, and means electrically connecting said electric reproducing device to said electrical receiving device, said reproducing device and said receiving device being mounted to swing about a common substantially horizontal axis and being mounted at opposite sides of said axis and being mcchanically interconnected in such manner that the receiving device partially counterbalances the reproducing device.

' 7. In combination with the tone arm of a phonograph, an electrical receiving device mounted at the outer end of said tone arm so as to swing about a substantially horizontal llO axis, means for directing sound `from said receiving device into said tone arm, an electrical reproducing device also mounted at the end of said tone arm so as to swing about the aforesaid axis, and means electrically connecting said reproducing device to said receiving device, said reproducing device and receiving device being located at opposite sides of said axis, and said reproducing device having means adapted to engage means 10 connected to said 'receiving device so as to cause the receiving device. to partially counter-balance the reproducing device.

In testimony whereof l have hereunto suhscribed my name this fourth day of May, 1926.

KENNETH I. MARSHALL. 

